Ultraviolet-curable resin composition for optical discs

ABSTRACT

There is provided an ultraviolet curing resin composition for an optical disk such as to improve the light resistance of reflective thin films made of silver or silver alloy and protect them against corroding and perform a high adhesive strength, in the optical disks. The composition comprises (1) a (meth)acrylate compound having a number average molecular weight of 700 to 3000 derived from epoxy resin, (2) a (meth)acrylate monomer having one or more of unsaturated ethylene groups, and (3) a polymerization initiator, such as 2,2-dimethoxy-2-phenylacetophenone, benzoylethyl ether and benzoylisobutyl ether, represented in the following general formula (I). Also, a tetrazole derivative may be additionally mixed into the composition.

TECHNICAL FIELD

[0001] The present invention relates to an ultraviolet curing resincomposition for optical disks.

BACKGROUND ART

[0002] An optical disk such as CD, CD-R and DVD records information on atransparent substrate thereof such as polycarbonate by pits and landsand forms an information recording layer by providing a reflective filmthat allows laser beam to bounce off of the surface of pits and landsfor reading out the information so as to have one or a plurality of suchinformation recording layers. In optical disks, aluminum, gold, silicon,silicon compounds such as SiC and SiN, or the like have beenconventionally formed into thin films by sputtering for being used asthe reflective film. Also, in an optical disk of a type such as to havea plurality of information recording layers and read out information inthese information recording layers from one side of the optical disk, atleast one of reflective layers is formed as a translucent reflectivefilm.

[0003] On the other hand, in the optical disk, an ultraviolet curingresin composition is used as a role of protecting the informationrecording layers for the purpose of performing surface protectivecoating on the above-mentioned reflective film. Also, in an optical diskof a higher recording density type such that two sheets of substratesare stuck to each other on backsides thereof, namely, so thattransparent substrates thereof face outward, an ultraviolet curing resincomposition is used for sticking the substrates together.

[0004] In the above-mentioned reflective film, thin films made of gold,silicon and silicon compounds have been used for translucent films ofDVD requiring the compatibility between high transmittance andreflectance, the problem is that gold costs high while silicon andsilicon compounds are troublesome to handle due to easy breaking andcracking and are oxidized in being formed into films so as tocontaminate a substrate surface of an optical disk. Accordingly, the useof thin films made of silver or silver alloy in which a slight quantityof gold, palladium, copper and the like are added to silver has beenstudied as substitutes for the above-mentioned thin films. For example,a reflective film for optical disks comprising silver alloy comprisingsilver as a major component is disclosed in U.S. Pat. No. 6,007,889.

[0005] Silver or the above-mentioned silver alloy, however, has aproblem of being essentially inferior in light resistance and not havinga sufficient durability due to easy corroding under the conditions ofhigh temperature and high humidity, so that thin films made of silver orthe silver alloy are used with difficulty as a reflective film forforming an information recording layer. In order to improve this, forexample, a technique is disclosed in Japanese Unexamined PatentPublication No. 2001-167478 for maintaining initial properties by usingan adhesive comprising an ultraviolet curing type composition with lowwater absorption and low moisture permeability for sticking thesubstrates together.

[0006] Conventional techniques, however, offer no solution to a problemsuch that silver and silver alloy are inferior in light resistance andthey also do not necessarily have sufficient adhesive force.

[0007] In view of the above-mentioned existing situation, the presentinvention is intended for providing an ultraviolet curing resincomposition such as to improve the light resistance of thin films madeof silver or silver alloy and protect them against corroding and performa high adhesive strength, in an optical disk in which an informationrecording layer is formed by the thin films made of silver or silveralloy.

DISCLOSURE OF THE INVENTION

[0008] The present invention is an ultraviolet curing resin compositionfor an optical disk in which an information recording layer is formed bythin films made of silver or alloy comprising silver as a majorcomponent, the ultraviolet curing resin composition for an optical diskcomprising (1) a (meth)acrylate compound having a number averagemolecular weight of 700 to 3000 derived from epoxy resin, (2) a(meth)acrylate monomer having one or more of unsaturated ethylenegroups, and (3) a polymerization initiator represented in the followinggeneral formula (I).

[0009] In the formula, R¹ denotes an alkyl group with a carbon number of1 to 4. R² denotes a hydrogen atom or an alkyl group with a carbonnumber of 1 to 4. R³ denotes a phenyl group or an alkyl group with acarbon number of 1 to 4.

[0010] In the present invention, the above-mentioned (meth)acrylatecompound (1) having a number average molecular weight of 700 to 3000derived from epoxy resin may be an adduct of ε-caprolactone-modified(meth)acrylate to epichlorohydrin-bisphenol A type (epi-bis type) epoxyresin. Also, in the present invention, a tetrazole derivative may beadditionally mixed. The present invention is hereinafter detailed.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] (1) A (Meth)acrylate Compound Derived from Epoxy Resin

[0012] The number average molecular weight of the above-mentioned(meth)acrylate compound (1) derived from epoxy resin is 700 to 3000. Anumber average molecular weight less than 700 weakens adhesive property,while a number average molecular weight more than 3000 deteriorateslight resistance and high temperature high humidity resistance. Thenumber average molecular weight is preferably 1000 to 2500. The numberaverage molecular weight could be measured by a method of gel permeationchromatography (GPC).

[0013] The above-mentioned (meth)acrylate compound derived from epoxyresin to be used includes, for example, epi-bis type epoxy resinderivative (meth)acrylate having a number average molecular weight of700 to 3000, which involves epi-bis type diglycidyl ether (meth)acrylatesuch as bis A diglycidyl ether di(meth)acrylate and bis F diglycidylether di(meth)acrylate; an adduct of ε-caprolactone-modified(meth)acrylate to epi-bis type epoxy resin such as an adduct ofε-caprolactone-modified (meth)acrylate to bis A diglycidyl ether (acaprolactone addition molar number of 1 to 10) and an adduct ofε-caprolactone-modified (meth)acrylate to bis F diglycidyl ether (acaprolactone addition molar number of 1 to 10); a combination of two ormore of these; and the like.

[0014] Among these, an adduct of ε-caprolactone-modified (meth)acrylateto epi-bis type epoxy resin is preferable. Above all, a (meth)acrylatecompound represented in the following general formula (II) is morepreferable.

[0015] In the formula, X denotes a methylene group, an ethylidene groupor an isopropylidene group. R denotes a direct bond or a divalentorganic group. n is an integer of 1 to 10, preferably 2 to 6. Theabove-mentioned divalent organic group may be, for example, a residuederived from divalent carboxylic acid with a carbon number of 2 or moresuch as a group represented in —OOCACO— (wherein A denotes a direct bondor a diester bond residue of divalent carboxylic acid with a carbonnumber of 3 or more). Among the above, the divalent carboxylic acid witha carbon number of 3 or more is not particularly restricted and involvesmalonic acid, succinic acid, adipic acid, maleic acid, itaconic acid,fumaric acid, phthalic acid, terephthalic acid, isophthalic acid,hexahydrophthalic acid, tetrahydrophthalic acid, dimer acid, and thelike.

[0016] A compound represented in the above-mentioned general formula(II) can be obtained, for example, by a method of reactingε-caprolactone-modified (meth)acrylate to which 1 to 10 mol ofε-caprolactone is added with epi-bis type epoxy resin.

[0017] The quantity of the above-mentioned (meth)acrylate compound (1)derived from epoxy resin to be mixed is preferably 10 to 80 parts byweight in 100 parts by weight of the resin composition, more preferably30 to 60 parts by weight in consideration of the viscosity of the resincomposition to be obtained.

[0018] (2) A (Meth)acrylate Monomer Having One or More of UnsaturatedEthylene Groups

[0019] The above-mentioned (meth)acrylate monomer having one or more ofunsaturated ethylene groups is not particularly restricted and may beone kind or two or more kinds of monofunctional or polyfunctional(meth)acrylate. Examples of the above-mentioned monofunctional orpolyfunctional (meth)acrylate are hereinafter listed.

[0020] Monofunctional (Meth)acrylate

[0021] Monofunctional (meth)acrylate is not particularly restricted andinvolves isobutyl (meth)acrylate, tert-butyl (meth)acrylate,phenoxyethyl (meth)acrylate, benzyl (meth)acrylate, tetrahydrofurfuryl(meth)acrylate, isooctyl (meth)acrylate, lauryl (meth)acrylate, stearyl(meth)acrylate, isobornyl (meth)acrylate, cyclohexyl (meth)acrylate,2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate,4-hydroxybutyl (meth)acrylate, 2-methoxyethyl (meth)acrylate,methoxytriethylene glycol (meth)acrylate, 2-ethoxyethyl (meth)acrylate,3-methoxybutyl (meth)acrylate, ethyl Carbitol™ (meth)acrylate,phenylglycidyl ether (meth)acrylate, 2-hydroxy-3-phenoxypropyl(meth)acrylate, tricyclodecane (meth)acrylate, dicyclopentenyl(meth)acrylate, dicyclopentenyloxymethyl (meth)acrylate,dioxolane-modified (meth)acrylate, and the like.

[0022] Difunctional (Meth)acrylate

[0023] Difunctional (meth)acrylate is not particularly restricted andinvolves 1,4-butanediol di(meth)acrylate, 1,5-pentanedioldi(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,9-nonanedioldi(meth)acrylate, 1,12-dodecanediol di(meth)acrylate, neopentyl glycoldi(meth)acrylate, (poly)ethylene glycol di(meth)acrylate,(poly)propylene glycol di(meth)acrylate,2-n-butyl-2-ethyl-1,3-propanediol di(meth)acrylate, bisphenol A ethyleneoxide 1 to 4 mol addition-modified di(meth)acrylate, bisphenol Apropylene oxide 1 to 4 mol addition-modified di(meth)acrylate, bisphenolF ethylene oxide 1 to 4 mol addition-modified di(meth)acrylate,bisphenol F propylene oxide 1 to 4 mol addition-modifieddi(meth)acrylate, tricyclodecane di(meth)acrylate, tricyclodecanedimethylol di(meth)acrylate, hydroxypivalic neopentyl glycoldi(meth)acrylate, ε-caprolactone-modified hydroxypivalic neopentylglycol di(meth)acrylate, and the like.

[0024] Trifunctional or More (Meth)acrylate

[0025] Trifunctional or more (meth)acrylate is not particularlyrestricted and involves tris((meth)acryloxyethyl)isocyanurate,trimethylol propane tri(meth)acrylate, trimethylol propane ethyleneoxide 1 to 4 mol added tri(meth)acrylate, trimethylol propane propyleneoxide 1 to 4 mol added tri(meth)acrylate, pentaerythritoltri(meth)acrylate, pentaerythritol tetra(meth)acrylate,glycerin-modified tri(meth)acrylate, dipentaerythritolhexa(meth)acrylate, and the like.

[0026] Among these, the following are preferable: tricyclodecane(meth)acrylate, tricyclodecane di(meth)acrylate, tricyclodecanedimethylol di(meth)acrylate, dicyclopentenyl (meth)acrylate,dicyclopentenyloxyethyl (meth)acrylate, isobornyl (meth)acrylate,hydroxypivalic neopentyl glycol di(meth)acrylate, trimethylol propanetri(meth)acrylate, trimethylol propane ethylene oxide 1 to 4 mol addedtri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritoltetra(meth)acrylate. Above all, dicyclopentenyl (meth)acrylate andtricyclodecane dimethylol di(meth)acrylate are more preferable due to asuperior curability on a resin surface and an end face of substrates tobe stuck together, which are easily affected by oxygen in the air to behindered from curing.

[0027] The quantity of the above-mentioned (meth)acrylate monomer (2)having one or more of unsaturated ethylene groups to be mixed ispreferably 20 to 90 parts by weight in 100 parts by weight of the resincomposition, more preferably 40 to 70 parts by weight.

[0028] (3) A Polymerization Initiator Represented in the General Formula(I)

[0029] The above-mentioned polymerization initiator represented in thegeneral formula (I) is not particularly restricted and involves2,2-dimethoxy-2-phenylacetophenone, benzoylethyl ether, benzoylisobutylether, a combination of two or more kinds of these, and the like.

[0030] Also, as required, a compound except the above-mentionedpolymerization initiator represented in the general formula (I) may beused together therewith; for example, one kind or two or more kinds of athioxanthone-based compound such as 2,4-diethylthioxanthone and2-isopropylthioxanthone, an acylphosphine oxide-based compound such as2,4,6-trimethylbenzoyldiphenylphosphine oxide andbis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide, and thelike.

[0031] The quantity of the above-mentioned polymerization initiatorrepresented in the general formula (I) to be mixed is preferably 0.2 to10 part(s) by weight in 100 parts by weight of the resin composition,more preferably 1 to 7 part(s) by weight.

[0032] In the case of using the compound except the polymerizationinitiator represented in the general formula (I), a proper quantitythereof can be mixed within a range of no hindrance to the object of thepresent invention.

[0033] A tetrazole derivative may be mixed as desired into theultraviolet curing resin composition for an optical disk of the presentinvention. The above-mentioned tetrazole derivative is not particularlyrestricted and involves 1-phenyl-5-mercaptotetrazole, 5-aminotetrazole,1-methyl-5-mercaptotetrazole, 5-phenyltetrazole,1-(2-dimethylaminoethyl) 5-mercaptotetrazole, a combination of two ormore kinds of these, and the like.

[0034] The quantity of the above-mentioned tetrazole derivative to bemixed is preferably 0.01 to 1 part by weight in 100 parts by weight ofthe resin composition, more preferably 0.05 to 0.5 part by weight. Thequantity to be mixed more than 1 part by weight brings the possibilityof deteriorating storage stability, while the quantity to be mixed lessthan 0.01 part by weight brings the possibility of insufficientlyoffering protective performance toward a reflective film made of silveror silver alloy.

[0035] Other additives may be mixed as required into the ultravioletcuring resin composition for an optical disk of the present invention.The above-mentioned additives are not particularly restricted and thefollowing may be used in accordance with purposes unless the object ofthe present invention is hindered, for example, a silane coupling agentsuch as alkyl-based, thiol-based, (meth)acrylate-based,isocyanate-based, and epoxy-based; a polymerization inhibitor such asmethoquinone and methyl hydroquinone; an antioxidant such as hinderedphenol, hindered amine, and phosphite; a leveling agent; an antifoamingagent; and the like.

[0036] Urethane (meth)acrylate and polyester (meth)acrylate may be mixedinto the ultraviolet curing resin composition for an optical disk of thepresent invention for the purpose of adjusting the properties such asviscosity and hardness unless the object of the present invention ishindered.

[0037] The ultraviolet curing resin composition for an optical disk ofthe present invention can be manufactured by mixing and stirring each ofthe above-mentioned components at normal temperature to a temperature ofapproximately 80° C., preferably under a reduced pressure, with the useof an organic solvent or without using it.

[0038] The ultraviolet curing resin composition for an optical disk ofthe present invention can be used appropriately for the optical disk inwhich an information recording layer is formed by thin films made ofsilver or alloy comprising silver as a major component. It should benoted that the constitution of the alloy comprising silver as a majorcomponent is not particularly restricted in the present specificationand includes, for example, alloy comprising silver slightly containingone kind or two or more kinds of gold, copper, rhodium, palladium,magnesium, nickel, aluminum, and the like. The composition of thepresent invention can be used for the optical disk having thin filmsmade of the above-mentioned components as well as an optical disk havingan information recording layer otherwise constituted such as an opticaldisk in which an information recording layer is formed by thin filmsmade of alloy comprising copper containing silver and thin films notcontaining silver. Also, raw materials of a substrate applied to theoptical disk are not particularly restricted and may be, for example,polycarbonate-based raw material, polyacryl-based raw material,amorphous polyolefin-based raw material, polyvinyl-based raw material,and the like.

EXAMPLES

[0039] The present invention is further detailed hereinafter by examplesand is not restricted thereto.

[0040] Raw materials used in the after-mentioned examples andcomparative examples are as follows:

[0041] Ebecryl 3708: an adduct of ε-caprolactone-modified acrylate tobis A diglycidyl ether, manufactured by DAICEL UCB Co., Ltd. (a numberaverage molecular weight of 2200, which is measured by a method of GPCwith a solvent of tetrahydrofuran, similarly measured hereinafter)

[0042] KRM 7856: an adduct of ε-caprolactone-modified acrylate to bis Adiglycidyl ether, manufactured by DAICEL UCB Co., Ltd. (a number averagemolecular weight of 1900)

[0043] VR 77: bisphenol A-type epoxy resin diacrylate, manufactured bySHOWA HIGHPOLYMER Co., Ltd. (a number average molecular weight of 800)

[0044] KRM 7811: aliphatic urethane diacrylate, manufactured by DAICELUCB Co., Ltd. (a number average molecular weight of 3500)

[0045] FA-511A: dicyclopentenyl acrylate, manufactured by HITACHICHEMICAL Co., Ltd.

[0046] HPP-A: hydroxypivalic neopentyl glycol diacrylate, manufacturedby KYOEISHA CHEMICAL Co., Ltd.

[0047] DCPA: tricyclodecane dimethylol diacrylate, manufactured byKYOEISHA CHEMICAL Co., Ltd.

[0048] IC 651 (the brand name of IRGACURE 651):2,2-dimethoxy-2-phenylacetophenone, manufactured by CIBA SPECIALTYCHEMICALS Inc.

[0049] IC 184 (the brand name of IRGACURE 184):1-hydroxycyclohexylphenyl ketone, manufactured by CIBA SPECIALTYCHEMICALS Inc.

[0050] IC 907 (the brand name of IRGACURE 907):2-methyl-1-[4-(methylthio)phenyl]-2-morpholino-propane-1-one,manufactured by CIBA SPECIALTY CHEMICALS Inc.

[0051] L-TPO (the brand name of LUCIRIN TPO):2,4,6-trimethylbenzoyldiphenylphosphine oxide, manufactured by BASF Co.,Ltd.

[0052] MMT: 1-methyl-5-mercaptotetrazole, manufactured by TOYO KASEIKOGYO Co., Ltd.

[0053] PMT: 1-phenyl-5-mercaptotetrazole, manufactured by TOYO KASEIKOGYO Co., Ltd.

[0054] IBXA: isobornyl acrylate, manufactured by OSAKA ORGANIC CHEMICALINDUSTRY Ltd.

EXAMPLES 1 TO 9 AND COMPARATIVE EXAMPLES 1 TO 4

[0055] Each of the raw materials was measured out into a flask inaccordance with the mixtures shown in Table 1 so as to be stirred at atemperature of 60° C. under a reduced pressure for 1 hour and be madeinto ultraviolet curing resin as uniform transparent liquid at each ofthe mixtures. It should be noted that the mixtures shown in Table 1 weredenoted part(s) by weight.

[0056] Two sheets of polycarbonate substrates having a thickness of 0.6mm were used for optical disks; one of them was a polycarbonatesubstrate on which a metallic reflective film having a thickness ofapproximately 15 nm was formed by sputtering silver alloy (the brandname of TTP32A, manufactured by Target Technology Co.), and the otherwas a polycarbonate substrate on which a metallic reflective film havinga thickness of 50 nm was formed by sputtering aluminum.

[0057] Approximately 2 g of the ultraviolet curing resin prepared abovewas applied between the above-mentioned two substrates of disks andextended by a spin coater at a rate of 3700 rpm for 3 seconds, so as toobtain a uniform adhesive layer having a thickness of approximately 40μm.

[0058] Thereafter, the adhesive layer was irradiated with ultravioletray having an intensity of 600 mJ/cm² by a metal halide lamp to becured, thereby obtaining a disk sample which consists of two substratesbounded together.

EVALUATING METHODS

[0059] The obtained disk samples which consists of two substratesbounded together were evaluated by the following methods. The resultsare shown together in Table 1.

[0060] Evaluation of Adhesive Property

[0061] The side of the adhesive layer of the disk samples was cut with acutter knife to peel away the two sheets of substrates, so that adhesiveproperty was evaluated by a peeling mode at the moment. The standard ofevaluation was as follows:

[0062] ◯: Adhesive strength was high and the metallic reflective filmwas peeled off the substrate.

[0063] Δ: The metallic reflective film was peeled off the adhesive layerwith difficulty, though.

[0064] ×: Adhesive force was weak and the metallic reflective film waseasily peeled off the adhesive layer.

[0065] Evaluation of High Temperature High Humidity Resistance

[0066] The optical disks remained untouched under the conditions of anatmosphere having a temperature of 85° C. and a relative humidity of 85%for 240 hours, so that defects such as corrosion and discoloration wereobserved by an optical microscope. The standard of evaluation was asfollows:

[0067] ◯: No change occurred as compared with the initial state.

[0068] ×: Defects such as discoloration and pinhole occurred as comparedwith the initial state.

[0069] Evaluation of Light Resistance

[0070] The optical disks were irradiated by a sunshine weatherometer (axenon lamp source) for 100 hours, so that the quality of lightresistance was determined by the rate of change in the reflectance ofthe metallic reflective film before and after being irradiated. Thestandard of evaluation was as follows:

[0071] A: The rate of decreases in the reflectance was less than 5%.

[0072] B: The rate of decreases in the reflectance was 5% to less than10%.

[0073] C: The rate of decreases in the reflectance was 10% to less than20%.

[0074] D: The rate of decreases in the reflectance was 20% or more.Comparative Examples Examples 1 2 3 4 5 6 7 8 9 1 2 3 4 Ebecry13708 5050 50 — 50 — — 50 50 — 50 50 — KRM7856 — — — 50 — 50 — — — — — — — VR77— — — — — — 50 — — — — — 50 KRM7811 — — — — — — — — — 50 — — — FA-511A50 50 50 50 30 — 50 — 50 50 — 50 — HPP-A — — — — — 50 — — — — 50 — —DCPA — — — — 20 — — — — — — — 50 IBXA — — — — — — — 50 — — — — — IC651 3  3  3  3  3  3  3  3  3  3 — — — IC184 — — — — — — — — — —  3 —  3IC907 — — — — — — — — — — —  3 — L-TPO — — — — — — — —   0.2 — — — — MMT—   0.2 —   0.2   0.2   0.2 —   0.2 — — — — — PMT — —   0.2 — — — — — —— — — — Adhesive ∘ ∘ ∘ ∘ ∘ ∘ Δ ∘ ∘ ∘ ∘ ∘ x Property High ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘∘ x ∘ ∘ ∘ Temperature High Humidity Resistance Light B A A A A A B A B DD D D Resistance

[0075] It was understood from the examples that the composition of thepresent invention sufficiently fulfilled all performances of adhesiveproperty, high temperature high humidity resistance, and lightresistance. In contrast, the comparative examples not employing theconstitution of the present invention exhibited an extremely low lightresistance among the performances. In addition, Comparative Example 4employing the mixture in conventional techniques exhibited extremely lowresults with regard to both of adhesive property and light resistance.

INDUSTRIAL APPLICABILITY

[0076] An ultraviolet curing resin composition for an optical disk ofthe present invention is constituted as described above, so as to vastlyimprove the light resistance of reflective thin films made of silver orsilver alloy as compared with conventional techniques and effectivelyprotect them against corroding. Also, an adhesive layer is flexible andoffers a high adhesive strength, leading to a contribution to animprovement in the mechanical strength of optical disks.

What is claimed is:
 1. (canceled)
 2. (amended) An ultraviolet curingresin composition for an optical disk comprising: (1) an adduct ofε-caprolactone-modified (meth)acrylate to epi-bis type epoxy resinhaving a number average molecular weight of 700 to 3000 derived fromepoxy resin; (2) a (meth)acrylate monomer having one or more ofunsaturated ethylene groups; and (3) a polymerization initiatorrepresented in the following general formula (I)

in the formula, R¹ denotes an alkyl group with a carbon number of 1 to4, R² denotes a hydrogen atom or an alkyl group with a carbon number of1 to 4, and R³ denotes a phenyl group or an alkyl group with a carbonnumber of 1 to
 4. 3. (amended) The ultraviolet curing resin compositionfor an optical disk according to claim 2, wherein a tetrazole derivativeis additionally mixed.
 4. (amended) The ultraviolet curing resincomposition for an optical disk according to claim 2, wherein saidadduct of ε-caprolactone-modified (meth)acrylate to epi-bis type epoxyresin (1) is a compound represented in the following general formula(II)

in the formula, X denotes a methylene group, an ethylidene group or anisopropylidene group, R denotes a direct bond or a divalent organicgroup, and n is an integer of 1 to
 10. 5. (amended) The ultravioletcuring resin composition for an optical disk according to claim 2,wherein said (meth)acrylate monomer (2) having one or more ofunsaturated ethylene groups is at least one kind selected from the groupconsisting of dicyclopentenyl (meth)acrylate, tricyclodecane dimethyloldi(meth)acrylate, and hydroxypivalic neopentyl glycol di(meth)acrylate.6. (amended) The ultraviolet curing resin composition for an opticaldisk according to claim 2, wherein said polymerization initiator (3)represented in the general formula (I) is at least one kind selectedfrom the group consisting of 2,2-dimethoxy-2-phenylacetophenone,benzoylethyl ether, and benzoylisobutyl ether.
 7. The ultraviolet curingresin composition for an optical disk according to claim 3, wherein thetetrazole derivative is at least one kind selected from the groupconsisting of 1-phenyl-5-mercaptotetrazole, 5-aminotetrazole,1-methyl-5-mercaptotetrazole, 5-phenyltetrazole, and1-(2-dimethylaminoethyl)-5-mercaptotetrazole.
 8. The ultraviolet curingresin composition for an optical disk according to claim 3, wherein aquantity of the tetrazole derivative to be mixed is 0.01 to 1 part byweight in 100 parts by weight of the resin composition.
 9. (amended) Theultraviolet curing resin composition for an optical disk according toclaim 2, wherein the ultraviolet curing resin composition for an opticaldisk is such that an information recording layer is formed by a thinfilm made of silver or alloy comprising silver as a major component.